Sustainable harvest of a threatened medicinal herb: Empirical evidence for spatially and temporally specific management of Neopicrorhiza scrophulariiflora

Abstract

Although over-exploitation and habitat loss limit sustainable management, medicinal and aromatic plants (MAPs) are essential for traditional health practices and as a source of cash income for rural communities around the world. In contrast to a general assumption that harvest negatively affects resource abundance, local knowledge and detailed empirical observations have shown that for some species, some harvest methods maintain or increase abundance. However, many management plans for wild-harvested MAPs lack empirical data on post-harvest recovery of density as well as key demographic measures such as fruit-setting and seed formation. To deepen our understanding of these important social-ecological dynamics across taxa, as well as to offer in-depth empirical data on a key economically important and threatened MAP, we applied controlled simulated-harvest field experiments to Neopicrorhiza scrophulariiflora in eight populations along an elevation gradient (3800–4700 m) in the Nepal Himalayas, including four populations in a restricted-access site and four in an open-access site in north-central and north-western Nepal. Each site with a different conservation regime exhibits distinctive ecological circumstances that enable assessing how environmental factors and the level of exploitation influence the characteristics of the plant populations. We hypothesized that not all levels of harvest would be harmful, and that restoration capacity would permit a sustainable level of harvest, subject to both social and ecological pressures (access and elevation). Experimental harvest treatments included removing 0 % (control), 25 %, 50 %, 75 %, and 100 % of the ramets from the experimental plots. We applied a mixed-effects model for repeated measures ANCOVA to determine if harvest treatments appeared to exert influence on each of the response variables at each site. Density and reproductive output varied significantly among the harvest treatments and covaried with the pre-harvest condition. At low elevations in the restricted-access site, both density and reproductive output recovered within three years after harvest of 50 % of the ramets, and within a single year after a 25 % harvest. To some extent, strong budding potential and re-sprouting from the old rhizomes compensated for negative harvest impacts. However, in the open-access site, recovery to the pre-harvest level was achieved only for a 25 % treatment after one year. Harvest recovery was slower at higher elevations (>4250 m), and plots harvested more intensively (>50 % extraction) recovered very slowly. Our results indicate that spatially and temporally specific harvesting strategies can be used to manage populations sustainably, supporting both wild plant populations and human livelihoods.